The chutes of a scraper conveyer at a fully-mechanized mining face are connected by dumbbell pins. In the coal mining process, the fully-mechanized mining equipment is pushed forward continuously as the coal mining face varies. The dumbbell pins bear a huge impact load in the pushing process, and may be worn and fractured easily under the extremely high tensile force. In the chute pushing process, the resistance force against pushing increases continuously, and the pushing stroke is increased continuously. If any dumbbell pin is fractured, the connection of middle chutes may be dislocated or broken, causing a chain reaction that may affect the normal production at the working face or even result in breakdown of the entire coal mining system, and bringing a severe potential safety hazard.
At present, in most mines in China, the conventional manual inspection method is still used to detect fracture failures of dumbbell pins. Owing to the complex working environment in a mine shaft, the large quantity of dumbbell pins, and the heavy inspection workload, it is difficult to detect and replace fractured dumbbell pins timely. Consequently, safe mining operation can't be ensured in the mine shaft. Existing fracture detection techniques, including electromagnetic induction techniques, optical fiber sensor detection techniques, strain sensor detection techniques, and traction return current detection technique, etc., have poor feasibility, because of the complex working environments in mine shafts, difficulties in underground deployment, and susceptibility to external interferences.